European patent document EP-PS 0 146 716 teaches how to construct the supporting structure of a vehicle body by using joining elements or "node connectors" to join the ends of a plurality of hollow-section extruded aluminum bearer members. The node connectors are formed as light metal castings. Depending upon the location of a particular bearer joint within the bodywork, the associated node connector may be provided with a specially molded and/or notched support surface for receiving an adjoining end portion of one or more extruded aluminum bearer members. Also, the note connector may consist of two half shell portions, which when combined, form a shell enclosure adapted to receivingly engage the end portions of two or more adjoining bearer members. In both cases, the joined ends of the bearer members are held in place by a weld and/or adhesive connection.
The greatest strain in a vehicle bodywork typically occurs at the bearer joints where several bearer members are joined together by a single node connector. Accordingly, high demands are placed on the strength and rigidity of these connection points. An especially critical connection point in the vehicle bodywork is the bearer joint located at the middle of the A post, Where a single node connector joins four frame components including the substantially vertically oriented lower A post portion (forward door post), a forwardly disposed and longitudinally directed front fender bearer (fender support brace), a lower transverse front windshield stringer, and an obliquely upward directed upper A post portion (forward roof post). Here, in particular, it is not possible to dimension the forward roof post with any given thickness in cross section, since to do so would impair the driver's vision. Thus, the node connection with the bottom end of the forward roof post represents the critical weak point of the roof and, consequently, the vehicle body as a whole in the roof imprint or vehicle rollover test.
A bearer connection between the forward roof post and the front section of a vehicle body is known, for example, from U.S. Pat. No. 2,520,074. In this document, the lower forward end portion of the forward roof post is downwardly directed through the region of the lower transverse window stringer and into the front section of the vehicle body. Once inside the vehicle body, it widens into a plate-shape member and is outwardly flanged along its side edges. The flanged side edges overlay an outside shroud panel and are connected thereto by spot welding. The entire arrangement in front of the forward roof post comprises relatively large surface area sheet metal components which overlay and connect onto one another. This document does not teach or suggest a self-supporting vehicle bodywork wherein individual frame pieces or bearer members are connected together by specific and separate joining elements or node connectors. Accordingly, this document does not address the problems associated with ensuring a stable bearer connection to a spatially separated joining element, and in particular a stable connection between an extruded aluminum bearer member and a cast aluminum node connector.
Japanese patent document JP-A-2 200 580 discloses another example of a bearer connection located at a middle region of the A post whereby the adjacent ends of three hollow section bearers (the forward door post, the forward roof post and the front fender bearer) are joined without using an additional joining element. In this design, the upper end of the forward door post is butt-connected to a longitudinally oriented and forwardly disposed fender bearer. A bottom end portion of a tubular front roof post is received within an appropriately sized cylindrical bore hole extending through both the walls of the fender bearer and the upper end of the forward door post and is welded in place along mutually supporting surfaces. A drawback with such a design, however, is that close tolerances for the machined parts are required to ensure a stable and accurately aligned connection, especially during the welding procedure. Close tolerances are sometimes difficult to control during the manufacturing process.